U.S. Pat. No. 4,159,365 discloses polyesters of terephthalic acid and phenylhydroquinone modified with up to 10 mole percent, based on total moles of units, of other aromatic or cycloaliphatic polyester-forming units. This 10 mole percent modification corresponds to 20 mole percent if based on the dicarboxylic acid alone or diol alone (the method we use to calculate our compositions). The use of a cyclohexanedicarboxylic acid is not disclosed. According to column 2, lines 4-6, "melt polymerization . . . is used for the polymer synthesis". Melt polymerization with phenylhydroquinone dipropionate causes trans-1,4-cyclohexanedicarboxylic acid to isomerize to give about 35 mole percent of the cis isomer, which reduces the liquid crystallinity of the polymer and thereby reduces the physical properties which can be attained. This isomerization of the trans to the cis dicarboxylic acid is unexpected, because the trans acid does not isomerize during the preparation of polyesters from trans-1,4-cyclohexanedicarboxylic acid and chlorohydroquinone diacetate or methylhydroquinone diacetate.
U.S. Pat. No. 4,118,372 discloses liquid crystalline copolyesters prepared with 1,4-cyclohexanedicarboxylic acid and substituted hydroquinones such as chlorohydroquinone diacetate. All polymers are prepared in the melt (column 5 and examples). The use of phenylhydroquinone is not disclosed.